[Intel-gfx] [PATCH 2/2] drm/i915: Use pipe state to tell when pipe is off

[Keith Packard]

On Sun, 3 Oct 2010 08:10:48 -0700, Jesse Barnes <jbarnes at virtuousgeek.org> wrote:

> Do these fixes help with the DP issues you've been seeing, Keith?
> Seems like the first one shouldn't change behavior since we ought to
> time out on waiting on vblank in that case, and the timeout is the same
> as the msleep we used to use.

The first one changes when the monitor sees the training message --
before the change, the training message would get sent before waiting
for the vblank, and could potentially mess up the monitor
synchronization with signals.

I tested this by turning an external DP monitor on/off repeatedly
without X running. Before the patch, the monitor would fail to sync once
in a while. With the patch, I haven't seen it fail. That's not to say
that it has actually fixed anything, just that it seems better.

The best feature of the patch is that it shortens the time it takes to
light up a DP pipe -- the code was always hitting the timeout instead of
seeing a vblank signal, so we'd get a 50ms delay instead of a couple of ms.

> The second one looks like a good change, but really the pipe off change
> is separate from the plane disable bug fix.

Yeah, yeah, I know. I should have split the patch into two pieces...

With these two patches in place, I'm not getting any timeouts while
waiting for vblank, which seems like a useful result, and should make
mode setting a tiny bit faster as well.

I've got a couple more changes to work on today:

 1) re-train the monitor when it gets unplugged and then plugged back
    in. Right now, if you kick the cable out, you're stuck fumbling
    around in the dark trying to run 'xrandr' again.
   
 2) send hotplug notification through the X server, at least for the
    'reliable' hotplug signals. Right now, when you run 'xrandr'
    after changing connections, gnome sees the connection status change
    event and 'does stuff', which frequently collides with the 'xrandr'
    command you're running. This is very confusing to users.

-- 
keith.packard at intel.com
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